Non-contacting position sensor using a rotating magnetic vector

ABSTRACT

A sensor for sensing the position of an object includes a magnet and a magnetic flux sensor. The magnet has dimensions that include a length, a width and a height. The magnet is adapted to generate a flux field. The flux field has a magnitude of flux and a flux direction. The flux direction changes along at least one of the dimensions. The magnetic flux sensor is mounted adjacent the magnet. The magnet provides a rotating magnetic field vector. A method for magnetizing a magnet to create the rotating magnetic field vector is also disclosed.

BACKGROUND OF THE INVENTION

I. Technical Field

This invention relates, in general, to non-contacting position sensors.More particularly, this invention relates to the magnetic configurationof a non-contacting position sensor that uses a magnetic flux sensor.

II. Background Art

Electronic devices are an increasingly ubiquitous part of everyday life.Electronic devices and components are presently integrated in a largenumber of products, including products traditionally thought of asprimarily mechanical in nature, such as automobiles. This trend isalmost certain to continue. To successfully integrate electronic andmechanical components, some type of interface between the twotechnologies is required. Generally, this interface is accomplishedusing devices such as sensors and actuators.

Position sensing is used to electronically monitor the position ormovement of a mechanical component. The position sensor produces anelectrical signal that varies as the position of the component inquestion varies. Electrical position sensors are an important part ofinnumerable products. For example, position sensors allow the status ofvarious automotive parts to be monitored and controlled electronically.

A position sensor must be accurate, in that it must give an appropriateelectrical signal based upon the position measured. If inaccurate, aposition sensor will hinder the proper evaluation and control of theposition of the component being monitored.

A position sensor must also be adequately precise in its measurement.The precision needed in measuring a position will obviously varydepending upon the particular circumstances of use. For some purposesonly a rough indication of position is necessary, for instance, anindication of whether a valve is mostly open or mostly closed. In otherapplications, more precise indication of position may be needed.

A position sensor must also be sufficiently durable for the environmentin which it is placed. For example, a position sensor used on anautomotive valve will experience almost constant movement while theautomobile is in operation. Such a position sensor must be constructedof mechanical and electrical components which are assembled in such amanner as to allow it to remain sufficiently accurate and precise duringits projected lifetime, despite considerable mechanical vibrations andthermal extremes and gradients.

In the past, position sensors were typically of the “contact” variety. Acontacting position sensor requires physical contact to produce theelectrical signal. Contacting position sensors typically consist ofpotentiometers to produce electrical signals that vary as a function ofthe component's position. Contacting position sensors are generallyaccurate and precise. Unfortunately, the wear due to contact duringmovement of contacting position sensors has limited their durability.Also, the friction resulting from the contact can result in the sensoraffecting the operation of the component. Further, water intrusion intoa potentiometric sensor can disable the sensor.

One important advancement in sensor technology has been the developmentof non-contacting position sensors. As a general proposition, anon-contacting position sensor (“NPS”) does not require physical contactbetween the signal generator and the sensing element. As presented here,an NPS utilizes magnets to generate magnetic fields that vary as afunction of position and devices to detect varying magnetic fields tomeasure the position of the component to be monitored. Often, a Halleffect device is used to produce an electrical signal that is dependentupon the magnitude and polarity of the magnetic flux incident upon thedevice. The Hall effect device may be physically attached to thecomponent to be monitored and move relative to the stationary magnets asthe component moves. Conversely, the Hall effect device may bestationary with the magnets affixed to the component to be monitored. Ineither case, the position of the component to be monitored can bedetermined by the electrical signal produced by the Hall effect device.

The use of an NPS presents several distinct advantages over the use ofthe contacting position sensor. Because an NPS does not require physicalcontact between the signal generator and the sensing element, there isless physical wear during operation, resulting in greater durability ofthe sensor. The use of an NPS is also advantageous because the lack ofany physical contact between the items being monitored and the sensoritself results in reduced drag upon the component by the sensor.

While the use of an NPS presents several advantages, there are alsoseveral disadvantages that must be overcome in order for an NPS to be asatisfactory position sensor for many applications. Magneticirregularities or imperfections may compromise the precision andaccuracy of an NPS. The accuracy and precision of an NPS may also beaffected by the numerous mechanical vibrations and temperature changeslikely be to experienced by the sensor. Because there is no physicalcontact between the item to be monitored and the sensor, it is possiblefor them to be knocked out of alignment by such vibrations. Amisalignment will result in the measured magnetic field at anyparticular location not being what it would be in the originalalignment. Because the measured magnetic field will be different thanthat when properly aligned the perceived position will be inaccurate.Linearity of magnetic field strength and the resulting signal is also aconcern.

Some of these challenges to the use of an NPS have been addressed inexisting devices, most notably the devices of U.S. Pat. Nos. 5,712,561and 6,211,668.

There remains, however, a continuing need for an improved positionsensor that displays minimal deviations due to changes in temperatureand that can be adapted for use over a wide range of measurementdistances and angles.

SUMMARY OF THE INVENTION

A feature of the invention is to provide a sensor that includes amagnet. The magnet has dimensions that include a length, a width and aheight. The magnet is adapted to generate a flux field. The flux fieldhas a magnitude of flux and a flux direction. The flux direction changesalong at least one of the dimensions.

Another feature of the invention is to provide a magnet that provides arotating magnetic field vector.

Yet another feature of the invention is to provide a method formagnetizing a magnet to create a rotating magnetic field vector.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a perspective view of a magnet in accordance with thepresent invention.

FIG. 2 illustrates a front elevation view of FIG. 1 with a magnetic fluxsensor.

FIG. 3 illustrates a side elevation view of FIG. 1.

FIG. 4 illustrates a front elevation view of FIG. 1 with an alternativemagnetic flux sensor location.

FIG. 5 illustrates a front elevation view of an alternative embodimentof a magnet and magnetic flux sensor in accordance with the presentinvention.

FIG. 6 illustrates a top plan view of an alternative embodiment of amagnet and magnetic flux sensor in accordance with the presentinvention.

FIG. 7 illustrates a side elevation view of FIG. 6.

FIG. 8 illustrates a magnetizing fixture and flux vector diagram for themagnet of FIG. 6 showing the rotating magnetic vector.

FIG. 9 illustrates the flux density for the magnet of FIG. 8 in theplane of the sensor at the nominal airgap between the magnet and sensor.

FIG. 10 illustrates a graph of magnetic flux density versus magnetposition for the magnet of FIG. 6.

FIG. 11 illustrates an alternative magnetizing fixture and flux vectordiagram for the magnet of FIG. 6 showing the rotating magnetic vector.

It is noted that the drawings of the invention are not to scale.

DETAILED DESCRIPTION

Referring to FIGS. 1-4 a non-contacting position sensor 20 is shown.Sensor 20 is adapted for use in monitoring the rotational position of anattached object that moves such as a shaft 22. Shaft 22 can be connectedto any moving object such as a butterfly valve in an engine throttlebody. Position sensor 20 includes a magnet 30 and a magnetic flux sensor50. Magnet 30 can be rotated through 360 degrees and can measurecontinuous rotation of an object.

As the magnetic field generated by the magnet 30 and detected by fluxsensor 50 varies sinusoidally with rotation, an electrical signal isproduced by sensor 50 that allows the position of the object to bemonitored to be ascertained.

Magnet 30 is cylindrical in shape and has an inner surface 32, an outersurface 34, end faces 35 and 36 and an interior cavity 38. Magnet 30generates a flux field that contains a flux vector that has a relativelyconstant flux density but a changing direction. A pole piece (not shown)may be used with magnet 30 to further control or direct the fluxgenerated by magnet 30. Magnetic flux sensor 50 can be a multi-axis halleffect device that is commercially available from MelexisMicroelectronic Systems of Concord, N.H. Other multi-axis hall effectdevices could also be used. A multi-axis hall effect sensor can measureflux direction by taking the ratio of flux density in 2 orthogonalplanes. Magnetic flux sensor 50 has several electrical leads 52 that areused to supply power, ground and an output signal from sensor 50.Magnetic flux sensor 50 has electrical leads 52. A printed circuit boardor lead frame (not shown) is adapted to hold flux sensor 50 in theproper position spaced from magnet 30 by an air gap 37. Air gap 37 islocated between magnet 30 and flux sensor 50. Magnetic flux from magnet30 is established across air gap 37 and is sensed by flux sensor 50.

In FIG. 2, the magnetic flux sensor 50 is mounted in cavity 38 adjacentto inner surface 32. Alternatively, as shown in FIG. 4, sensor 50 can bemounted outside the magnet adjacent outer surface 34. Magnet 30 can beformed of any suitable magnetic material, such as samarium cobalt,neodymium-iron-boron or ferrite.

In another embodiment, shown in FIG. 5, only half of the magnet 30 maybe used. Semi-cylindrical magnet 40 has an inner surface 44, an outersurface 42 and end faces 46 and 48. Magnetic flux sensor 50 can bemounted adjacent interior surface 44. Magnet 40 can be used to measureup to 180 degrees of rotation of an attached object.

Turning to FIGS. 6 and 7, another embodiment of a magnet 60 is shown.Magnet 60 has a rectangular shape and is in the form of an elongated barhaving outer surfaces 62, 64, 66, 68, 70 and 72. Magnet 60 hasdimensions including a length L, a width W and a height H. Magnetic fluxsensor 50 can be mounted adjacent surface 62. Magnet 60 can be used tomeasure linear travel of an attached object.

Alternatively, magnet 60 can be made from thin bonded ferrite andsubsequently bent and affixed into a shape similar to magnet 30. In thismanner, magnet 60 can be used to measure the rotary position of anattached object. Further, if magnet 60 is a flexible bonded ferritemagnet material, it can be formed into a ring shape for use in a rotarysensor and may be fitted into a housing. Magnet 60 may also be formed bymolding. Magnet 60 can be magnetized in a straight shape and then bentinto a circular shape. Alternatively, magnet 60 could also be magnetizedafter it has been formed into a round shape.

Magnet 60 can also be used to make a through-hole sensor in which ashaft extends through a hole along the axis of rotation of the magnet.This design allows the flexibility to place a magnetic flux sensor onthe inside or outside of the magnet as needed.

FIG. 8 illustrates a more detailed view of bar magnet 60 showing amagnetization pattern 75 and flux vectors generated by magnet 60. Forthe convenience of understanding the operation of the present invention,magnet 60 is designated in several adjacent segments or sections 80A,80B, 80C, 80D, 80E, 80F, 80G, 80H, 80I, 80J and 80K. Sections 80A-K willbe used to illustrate how the flux vectors generated by magnet 60 varyor change with position. In reality, these segments do not exist withinmagnet 60 and the change in the flux vector is continuous when movingalong at least one dimension of magnet 60. Each segment 80 has anassociated flux vector 90. Flux vectors 90A, 90B, 90C, 90D, 90E, 90F,90G, 90H, 90I, 90J and 90K each have a flux magnitude and a fluxdirection.

The flux direction continuously changes or rotates when moving fromsegment 80A towards segment 80K along length L. A reference axis of X, Yand Z directions are shown in the lower left hand corner of FIG. 8. Therotating flux direction is created by rotating the magnetizationdirection within magnet 60. The flux direction in FIG. 8 is shownchanging in the X-Z plane. Other planes can also be used as will bediscussed later.

Referring to FIG. 9, the flux vectors 90 for magnet 60 were generatedusing a computer simulation program. The flux vectors 90 are shown at adistance of 0.1 inch from the magnet surface 62. A sensing plane 150 wasused to simulate the position of flux sensor 50 as magnet 60 is movedalong length L. Flux sensor 50 positioned 0.1 inch from the magnetsurface would detect this changing flux vector as magnet 60 is movedalong length L.

It is noted in FIG. 9 that magnetic vectors 90 have a sizable magneticfield called Bz or a Z axis component as one moves from the bottomsurface 72 to the top surface 70 of the magnet. The magnetic field B ismeasured in Gauss or Tesla. This magnetic field Bz component isparasitic to the magnetic field Bx & By components in the X and Ydirections and is minimized near the bottom surface 72 of the magnet 60.

Flux sensor 50 creates three intermediary electrical signals Sx, Sy andSz that are proportional to the strength of the magnetic field in eachdirection. Signals Sx, Sy and Sz are internal to and contained in sensor50. An electrical output signal is provided on one of the electricalleads 52. Sensor 50 calculates the output signal by using a proportionof the arctangent of the ratio of these flux densities. This signal hasa saw-tooth shape and represents the flux direction that is independentof flux density amplitude variation. For the magnet shown in FIGS. 8 and9, the Sx and Sz signals are of interest because the flux direction isrotating in the X-Z plane.

FIG. 10 is a graph of magnetic field strength as a function of linearposition along magnet length L. FIG. 10 shows the output signals Sx andSz from sensor 50 corresponding to the Bx and Bz flux vectors for magnet60. The Sy signal is not shown in FIG. 10 as it is not needed in orderto determine the position of magnet 60.

The arctangent of the ratio for a line down the vertical midpoint of thesensing plane is shown in FIG. 10 and is labeled Arctan. It is notedthat the Arctan line is linear and has a period P. The length of periodP corresponds to the Length L of the magnet.

FIG. 8 also shows a magnetization fixture 100 that is needed to createthe magnetization pattern 75 in magnet 60. Magnetization FIG. 100includes a wire 101 that has ends 102 and 104. Wire 101 can be a copperwire that is connected to a source of electrical power (not shown).Current 110 flowing through wire 101 causes a magnetic fieldcorresponding to magnetization pattern 75 to be imposed upon andimparted to magnet 60. It is noted that the distance between wire ends102 and 104 and the distance between the magnet and wire allows fortailoring of the period of the vector rotation or how fast the fluxvector rotates along the length of the magnet.

The present invention has several advantages. One advantage is that theflux density of flux vectors 90A-K results in the output signal sensedby flux sensor 50 being independent of all amplitude related variationsof the magnet, temperature variation being one of the variations.Therefore, additional temperature compensation devices and circuits arenot needed. Another advantage is that the sensing period of sensor 20can easily be changed. The period of the vector rotation or how fast theflux vector rotates along the length of the magnet can be changed byadjusting magnetization fixture 100. The period can be changed byselecting the physical dimension and spacing of wire 101.

It should be appreciated that the present invention may be readilyadapted for use in measuring rotations of any angular dimension or inmeasuring any linear movements. The invention may be used to measurerotations of three hundred and sixty degrees or more, using anelectronic counter for multiple revolutions.

Referring to FIG. 11, an alternative magnetizing fixture 200 and fluxvector diagram for magnet 60 is shown. FIG. 11 illustrates amagnetization pattern 275 and flux vectors generated by magnet 60. Forthe convenience of understanding the operation of the present invention,magnet 60 is designated in several adjacent segments or sections 80A,80B, 80C, 80D, 80E, 80F, 80G, 80H, 80I, 80J, 80K, 80L and 80M. Sections80A-M will be used to illustrate how the flux vectors generated bymagnet 60 vary or change with position. In reality, these segments donot exist within magnet 60 and the change in the flux vector iscontinuous when moving along at least one dimension of magnet 60. Eachsegment 80 has an associated flux vector 290. Flux vectors 290A, 290B,290C, 290D, 290E, 290F, 290G, 290H, 290I, 290J, 290K, 290L and 290M eachhave a flux magnitude and a flux direction.

The flux direction continuously changes or rotates when moving fromsegment 80A towards segment 80M along length L. A reference axis of X, Yand Z directions are shown in the lower left hand corner of FIG. 11. Therotating flux direction is created by rotating the magnetizationdirection within magnet 60. The flux direction in FIG. 11 is shownchanging in the X-Y plane. Other planes can also be used such as the Y-Zplane.

FIG. 11 also shows a magnetization fixture 200 that is needed to createthe magnetization pattern 275 in magnet 60. Magnetization fixture 200includes a wire 202 that has ends 204 and 206 and U-shaped portions 254and 256. Wire 202 can be a copper wire that is connected to a source ofelectrical power (not shown). Current 252 flowing through wire 201causes a magnetic field corresponding to magnetization pattern 275 to beimposed upon and imparted to magnet 60. It is noted that the distancebetween wire ends 204 and 206 and the distance between U-shaped sections256 and 258 and the distance between the magnet and wire allows fortailoring of the period of the vector rotation or how fast the fluxvector rotates along the length of the magnet.

Although the invention has been taught with specific reference to theseembodiments, someone skilled in the art will recognize that many otherchanges can be made in form and detail without departing from the spiritand the scope of the invention. The described embodiments are to beconsidered in all respects only as illustrative and not restrictive. Thescope of the invention is, therefore, indicated by the appended claimsrather than by the foregoing description. All changes which come withinthe meaning and range of equivalency of the claims are to be embracedwithin their scope.

1. A sensor comprising: a) a magnet including a length and a heightdefining a longitudinal plane and a width defining an interior; b) themagnet being adapted to generate a rotating flux vector in the interiorof the magnet, the flux vector having a magnitude and a direction and aplane of rotation; and c) the direction of the flux vector in theinterior of the magnet continuously changing along the length of themagnet, the plane of rotation of the rotating flux vector being in thesame orientation as the longitudinal plane of the magnet.
 2. The sensorof claim 1, wherein the flux vector comprises at least two orthogonalcomponents.
 3. The sensor of claim 1, wherein a magnetic flux sensor ismounted adjacent the magnet, the magnetic flux sensor being adapted tosense the flux direction.
 4. The sensor of claim 3, wherein the magneticflux sensor is insensitive to temperature changes in the magnet.
 5. Thesensor of claim 3, wherein the magnetic flux sensor is insensitive toamplitude related variations.
 6. The sensor of claim 3, wherein themagnetic flux sensor comprises a hall effect device.
 7. The sensor ofclaim 3, wherein the magnet is affixed to a movable object such thatwhen the object moves the magnet moves relative to the magnetic fluxsensor.
 8. The sensor of claim 7, wherein the movable object movesrotationally.
 9. The sensor of claim 7, wherein the movable object moveslinearly.
 10. A sensor comprising: a) a magnet defining a plane and aninterior and adapted to generate a flux field whose direction in theinterior of the magnet changes continuously in the plane of the magnet;and b) a magnetic flux sensor mounted in proximity to the magnet, themagnet and the magnetic flux sensor being moveable relative to eachother in a direction of measurement, the magnetic flux sensor beingadapted to sense the direction of the flux and generate an electricalsignal that is representative of the direction of the flux, thedirection of the flux field being at least partially in the samedirection as the direction of measurement.
 11. The sensor of claim 10,wherein the magnet is attached to a moveable object for sensing theposition of the movable object.
 12. The sensor of claim 10, wherein thedirection of the flux has an adjustable rotation period.
 13. A sensorcomprising: a) a magnet with a flux having a magnitude and a directionwithin the magnet, the direction of the flux within the magnet changinga plurality of times along the magnet; and b) a sensor for sensing thedirection of the flux and generating an electrical signal that isrepresentative of the direction of the flux in response to movement ofthe magnet and the sensor in a direction relative to each other, thedirection of the flux within the magnet being at least partially thesame as the direction of the movement of the magnet and the sensorrelative to each other.
 14. The sensor of claim 13, wherein the magnetis coupled to an object whose position is desired to be sensed.
 15. Thesensor of claim 13, wherein the flux direction has a rotation periodthat can be adjusted.
 16. The sensor of claim 13, wherein the magnet isring-shaped.
 17. A sensor comprising: a) a magnet defining alongitudinal axis and generating a flux vector therewithin having a fluxmagnitude and a variable flux direction, the flux direction continuouslychanging along and in the same plane as the longitudinal axis of themagnet; and b) a magnetic flux sensor mounted in proximity to themagnet, the magnet and the magnetic flux sensor being moveable relativeto each other, the magnetic flux sensor being adapted to sense thevariable flux direction and generate an electrical signal representativeof the variable flux direction.
 18. The sensor of claim 17, wherein arate of change of the variable flux direction can be adjusted.